The present invention relates to a method of manufacturing a structural body and an apparatus therefor; and, more particularly, the invention relates to a friction stir method of welding elements of a structural body and a friction stir welding apparatus therefor.
Two members to be subjected to friction stir welding have a raised portion at one side thereof where they are abutted, and, from a side of the raised portion, a rotary tool is inserted into a joint between the members and then a friction stir welding is carried out. In friction stir welding, when a gap exists between two members to be subjected to the friction stir welding process, a reduced thickness of the two members by the material contributed by the raised portion is compensated.
After the friction stir welding, the remainder of the raised portion of the two members that is no longer needed is cut off and removed in such a way that the outer face of the member formed by friction stir welding is flat and smooth. This technique is disclosed in Japanese application patent laid-open publication No. Hei 09-309164 (EP 0797043 A2).
Further, a cutter may be provided which operates in a radial direction of the rotary tool. The small diameter portion of the rotary tool is inserted into the joint between the members and a boundary formed between the large diameter portion and the small diameter portion of the rotary tool is brought into contact with the members to be subjected to the friction stir welding. The cutter projects toward a side of the large diameter portion of the rotary tool from the boundary. This cutter can cut off or delete a burr which is generated as a result of the friction stir welding. This technique is disclosed in Japanese application patent laid-open publication No. Hei 10-71477 (U.S. Pat. No. 5,794,835, EP 0810055 A1).
Further, the rotary tool and the cutter may be provided separately, and, as the cutter, an end milling member may be used. This technique is disclosed in Japanese application patent laid-open publication No. Hei 10-175089.
When the members having a raised portion along one side thereof are subjected to friction stir welding, a burr is typically generated at the welding joint. Further, at least a part of the raised portion of the member subjected to the friction stir welding is left. In a case where the raised portion is formed on the outer face of a structural body, it is necessary to remove the residual raised portion. Thus, to the rotary tool, a cutter is attached to cut off any excessive raised portion and the burr on the weld joint as the welding occurs. However, such cutting tends to produce chips, the existence of which makes it difficult to carry out a good friction stir welding.
The above-stated considerations will be explained in more detail. To a front portion in an advancing direction of the rotary tool, an optical sensor is provided for detecting optically the raised portion of the member being subjected to the friction stir welding. This optical sensor can detect the width of the two abutting raised portions of the members, and thereby guide the rotary tool to a position at the center thereof where the welding joint is located. Further, the optical sensor can detect the height of the raised portion of the members, and, subject to that determination, the amount the rotary tool should be inserted into the joint of the members to be welded can be determined suitably. However, the detection range of the optical sensor is affected when chips enter the working area, making it impossible to carry out a precise detection.
Further, at a front portion and at a rear portion of the rotary tool, rollers are installed, which rollers ride on the surface of the raised portion of the members being subjected to friction stir welding or the vicinity of the raised portion relative to a bed. Since chips collect at the rear portion of the rotary tool, the chips tend to obstruct movement of the rear roller. For this reason, the member being subjected to the friction stir welding is likely to be damaged due to the presence of these chips.